The present invention relates to the operation of conveyor belts, such as those known as endless belts supported by a series of parallel support rollers, and more particularly to a system for maintaining alignment of a conveyor belt during operation.
Belt tracking, or maintaining a conveyor belt moving in a generally straight, designated path, is a problem in any industry that uses conveyor belts. It is often not a major problem but rather a maintenance nuisance that progressively over time becomes a major cost.
Several factors can affect belt tracking. Misalignment of the rollers will cause corresponding belt tracking problems. Also, uneven loading of conveyor belts may also cause tracking problems, as well as unequal driving forces across the belt width.
Further, it is common for a tracking device for conveyor belts to fail prematurely. Carry back material (material that has not been removed by a belt scraper at the conveyor discharge point) for instance may cause material build up and result in the rollers and pivot mechanism to seize into a misalignment position.
Various conveyor belt systems have been developed over the years with design considerations relating to accurate tracking. With respect to any belt, the ability to track will vary considerably, and this in turn is due to a number of variables involved in the production of a belt itself. Compounding this problem is the possibility that the belt might be stretched upon installation. Over correction during initial tracking adjustments may result in stretching the belt in inappropriate areas. It has also been observed that existing tracking devices will only align a conveyor belt once it is way off center, thereby resulting in serious damage and down time.
In U.S. Pat. No. 7,051,867, which is incorporated by reference, a suitable belt alignment system includes a pair of pivoting members, each mounted on a corresponding support bracket. Each pivoting member is configured for supporting one of a pair of tracking rollers at a corresponding tracking roller shaft end. Each shaft end is pivotally and non-rotatably attached to a corresponding pivoting member by a ball bushing mounted in a corresponding one of the pivoting members.
In U.S. Pat. No. 8,376,127, which is also incorporated by reference, a belt alignment system includes a pair of pivoting members, where each pivoting member is configured for supporting one of a pair of tracking rollers at a corresponding tracking roller shaft end. The shaft ends are each pivotally and non-rotatably attached to a corresponding pivoting member by a bushing mounted in a rotatable block in a corresponding one of the pivoting members.
In U.S. Pat. No. 9,033,135, which is also incorporated by reference, a belt alignment system includes a support bracket and two racking rollers independently mounted to the support bracket where the tracking rollers include a shaft being coupled to pivoting members on one end and a center support on the other end of the shaft. Movement of the pivoting members causes the tracking rollers to pivot relative to the center support. A guide control bar having two ends is pivotally connected to a corresponding torque arm at each end, where the guide control bar includes a pair of guide rollers positioned at both edges of the conveyor belt.
In applications using a wide conveyor belt, the shaft including the tracking rollers that supports the belt should be equal to or wider than the belt to provide sufficient support for the belt. The added weight from the wider belt and any residual product or dirt remaining on the belt, increases the stress forces on the bushings at the shaft ends, which increases the wear on the bushings and the risk of malfunction or failure. Also in conveyor systems including cupped or v-shaped conveyor belts, belt alignment systems having a single shaft only provide support at the central portion of the belts that contact the rollers. The more weight on a steering roller, the more traction and friction between the rollers and the belt. As a result, the force from the weight of the belt is greatest at the center of the shaft between the bushings which can lead to bending or failure of the shaft.
Thus, there is a need for a belt alignment system that addresses the above-listed operational drawbacks of existing units.